Balancing devices of the type specified above for dynamically measuring imbalances on a rotation element are generally known. In particular with turbochargers it is necessary to measure rotation speeds of between 20,000 and over 200,000 revolutions a minute and the imbalances and vibrations that occur here.
For this purpose, it is proposed in the prior art to insert the rotation element—here in the form of a core assembly of a turbocharger which is composed of a compressor wheel and a turbine wheel which are coupled to one another by a shaft with a shaft nut for dynamically measuring imbalances in one or more planes—into the balancing device. For this purpose, the core assembly is pushed into a central receiver formed in the balancing device and is fixed therein. Next, the rotation element is set in rotation, and imbalances of the rotation element are detected by sensors.
The core assembly is often fastened in the balancing device by bolts attached to the central receiver. However, it is a disadvantage of this type of solution that in each case it takes a great deal of time to fix the core assembly in place, and this considerably extends the cycle times of the balancing device.
In order to reduce the cycle times, it has been proposed in the prior art to fix the core assembly to a support structure in the central receiver, the support structure being displaced parallel to the axis of rotation of the core assembly. However, this form of support structure is very cumbersome and solid, and so increases the masses to be accelerated in the balancing process, and this may lead to falsification of the balancing result.
In order to overcome this problem, it is proposed in U.S. Pat. No. 9,261,110 B2 to also provide a base body on which a core assembly is received in a central receiver formed in the base body. Here the base body is in the form of a decoupling element which has a basic structure which elastically surrounds a supporting structure. The elasticity is achieved by providing spring elements. This means that structures are cut out of the decoupling element by means of wire-electro discharge machining such that the base element and the supporting element are elastically connected to one another by springs formed by the wire-electro discharge process.
However, a disadvantage of this design of decoupling element is that the core assembly must be fastened to the structure by hydraulic cylinders fastened to the base element. In order to counteract an associated increase in mass, in U.S. Pat. No. 9,261,110 B2 it is proposed to provide window elements between the hydraulic cylinders fixed to and pre-stressed on the decoupling element and the core assembly that is to be fixed, which window elements should enable resilient punctiform fixing of the core assembly within the central receiver. However, it is very complex to produce these windows reproducibly.
On the other hand, if the balancing device is not fitted correctly, for example if the core assembly is not inserted, there is the risk that, due to the radial forces exerted by the hydraulic cylinders upon the axial fixing of the core assembly and the associated forces exerted upon the decoupling element, the hydraulic cylinders as well as the window elements will move into the receiver so that the spring elements formed between the base structure and the support structure will ultimately break. As a consequence, the entire decoupling element made in one part must be replaced because the spring elements provided between the base element and the supporting element cannot be replaced.